Method dependence of Antarctic atmospheric blocking and implications for large-scale circulation and climate extremes

Atmospheric blocking is a key driver of persistent circulation anomalies and associated extreme events in the Southern Hemisphere, yet its characteristics around Antarctica remain poorly understood due to methodological diversity and the absence of a consolidated, long-term dataset. This contribution investigates how methodological choices in blocking detection influence the inferred characteristics of Antarctic blocking and discusses the implications for large-scale circulation variability and climate extremes. Using ERA5 reanalysis for the period 1979 to 2024, we apply several established blocking diagnostics based on geopotential height and potential vorticity within a unified spatiotemporal framework. By standardising filtering, event identification, tracking, and aggregation procedures, we isolate differences that arise specifically from the diagnostic formulation rather than from implementation details. The comparison reveals substantial method dependent variability in blocking frequency, spatial extent, persistence, and intensity, particularly at high southern latitudes where circulation regimes differ from classical midlatitude blocking. Geopotential height based diagnostics identify a broader range of quasi stationary anticyclonic anomalies, including events extending toward the Antarctic continent, while potential vorticity based diagnostics isolate fewer and more spatially confined events associated with dynamically coherent upper level disturbances near the polar vortex. These methodological contrasts have direct implications for how blocking related climate extremes are interpreted, including links to temperature anomalies, moisture intrusions, and surface melt episodes. Differences in diagnosed event duration and location can substantially alter the attribution of extreme conditions to blocking regimes. Ongoing work examines how blocking characteristics identified by different diagnostics relate to variability in large scale circulation modes such as the Southern Annular Mode and ENSO, highlighting the importance of methodological awareness when assessing teleconnections and long term variability. Overall, the results demonstrate that Antarctic atmospheric blocking cannot be fully characterised by a single diagnostic perspective and that method dependence must be explicitly considered in studies of polar circulation variability, climate extremes, and future change.